1. Field of the Invention
The present invention relates to a polymer having a novel structure, and in particular, relates to a polymer having electron transportability. The present invention also relates to an electrophotographic photosensitive member containing this polymer, and a process cartridge and an electrophotographic apparatus having the electrophotographic photosensitive member.
2. Description of the Related Art
Electronic devices such as electrophotographic photosensitive members and solar batteries require materials for effectively transporting only electrons or holes. Hole-transporting materials which transport only holes at a high efficiency have been widely used for electrophotographic photosensitive members. Charge-transporting materials also have been used for ozone-free electrophotographic photosensitive members. Examples of known charge-transporting materials include organic materials, such as a diphenoquinone derivative (as disclosed in Japanese Patent Laid-Open No. 3-216662), an imide derivative (as disclosed in Japanese Patent Laid-Open No. 5-27469), and a TNF derivative (as disclosed in Japanese Patent Laid-Open No. 2-203352); and low.molecular weight compounds, e.g. a charge-transporting complex comprising an acceptor compound and a donor compound (as disclosed in Japanese Patent Laid-Open No. 1-314253). Further, polymeric compounds having electron transportability are disclosed in Japanese Patent Laid-Open Nos. 2-123370 and 4-353858.
Charge-transporting materials, however, have not been disclosed as much as hole-transporting materials. The low molecular weight compound must be dissolved into an appropriate resin in the film forming process. However, the solubility or compatibility of the charge-transporting material in the resin matrix is limited. When a high content of the charge-transporting material is added, the crystals of the charge-transporting material are precipitated. On the other hand, a low content of the charge-transporting material does not have sufficient electron transportability. Since the low molecular weight compound does not have satisfactory mechanical strength, scuffs and cracks form in use. Most of the polymeric compounds are a side chain type in which side chains have electron transportability. In side chain type polymeric compounds, cohesiveness between molecular chains is low, and this inhibits improvement in the electron transportability.